JP3634406B2 - Active silencer - Google Patents

Description

ただし、Ｎ＋１個の音源はすべて音響の分野でいうところの呼吸球、すなわちモノポ―ル音源とする。（１） 式において、Ｒ_ｉｊは放射抵抗、Ｖ_ｉ 、θ_ｉ は音源ｉの振動速度、位相を表す。
【００１９】
音源ｉの音の強さ、すなわち体積速度をＡ_ｉ とすると、
Ａ_ｉ ＝４ πｒ_ｉ ^２ ｜Ｖ_ｉ ｜ （ｒ_ｉ ：振動半径） …（２）
であることから、全音響パワ―Ｗ_ａｌｌ は、各音源の体積速度（振幅）と位相により変化することが判る。
【００２０】
そこで、空間内に設置した音検知手段（評価用マイク）で音源の合成音を検出し、この音検知手段での音圧を最小にするような制御を行い、各付加音源の体積速度と位相を変化させる。
【００２１】
制御後の体積速度と位相は以下の（３） 式、（４） 式、（５） 式によって決定されるので、図２に示すように、音源Ｐの周囲全体の音響パワ―を低減させるには音検知手段Ｍおよび各付加音源Ｓ_１ ，Ｓ_２ ，…Ｓ_Ｎ の配置が重要であることが判る。
【００２２】
【数２】

ただし、ρ：空気密度、ω：角振動数、ｈ_ｉ ：ｉ番目の付加音源から音検出手段Ｍまでの距離、ｋ：波数、θ_ｉ ：ｉ板目の付加音源の位相、θ_１ ：音源Ｐの位相である。
【００２３】
そこで、図３に示すように、２個の付加音源Ｓ_１ ，Ｓ_２ を設けた場合について考えて見る。
【００２４】
今、２つの付加音源Ｓ_１ ，Ｓ_２ が同位相で、音源Ｐから等距離に配置されている条件のもとでは、音源Ｐに対する付加音源Ｓ_１ ，Ｓ_２ の位相θと体積速度比α（Ａ２ ／Ａ１ ）とは以下の式で表される。
【００２５】
【数３】

したがって、制御後の音響パワ―低下量η（ｄＢ）は次式となる。
【００２６】
【数４】

本発明の一つの例に係る能動消音装置では、たとえば図４（ａ） に示すように、正三角形の各頂点に音源Ｐ、付加音源Ｓ_１ ，Ｓ_２ 、音検知手段Ｍがそれぞれ位置するように配置しているので、上述した制御を行うと、（６） 式および（７） 式から音源Ｐに対する付加音源Ｓ_１ ，Ｓ_２ の位相が１８０度、体積速度比が１／２に近づき、音源Ｐから涌き出した流体と同じ量だけ付加音源Ｓ_１ ，Ｓ_２ で吸い込ませることができ、音源Ｐから放射される音響パワ―そのものを最小にできることになる。
【００２７】
なお、図４（ｂ） に示すように、音源Ｐの両側に付加音源Ｓ_１ ，Ｓ_２ を配置するとともに、音源Ｐから十分離れ、かつ付加音源Ｓ_１ ，Ｓ_２ から等距離位置に音検出手段Ｍを配置すると、音源Ｐから音検出手段Ｍまでの距離ｈ_１ と付加音源Ｓ_１ ，Ｓ_２ から音検出手段Ｍまでの距離ｈ_２ ，ｈ_３ との差が零に近付くので、（６） 式および（７） 式における（ｈ_１ −ｈ_２ ）および（ｈ_１ −ｈ_３ ）の項を零に近付けることができる。したがって、この場合も上述した制御を行うと、音源Ｐに対する付加音源Ｓ_１ ，Ｓ_２ の位相が１８０度、体積速度比が１／２に近づき、音源Ｐから涌き出した流体と同じ量だけ付加音源Ｓ_１ ，Ｓ_２ で吸い込ませることができ、音源Ｐから放射される音響パワ―そのものを十分に低減できる。
【００２８】
さらに、実験によると、図４（ｃ） に示すように、音源Ｐの両側で、音源Ｐを通る線上に音源Ｐから距離ｄだけ離して付加音源Ｓ_１ ，Ｓ_２ を配置するとともに、同じ線上で音源Ｐからｘ＝０．６ ｄだけ離れた位置やｘ＞ｄの位置に音検出手段Ｍを配置して上述した制御を行なっても音源Ｐから放射される音響パワ―そのものを低減できる。
【００２９】
また、図４（ａ） ，（ｂ） ，（ｃ） の場合、後述するように、音源Ｐと付加音源Ｓ_１ ，Ｓ_２ との間の距離ｄが小さいほど効果的である。したがって、付加音源Ｓ_１ ，Ｓ_２ が大きい場合や、熱などの影響で付加音源Ｓ_１ ，Ｓ_２ を音源Ｐに近付けることができない場合には、付加音源Ｓ_１ ，Ｓ_２ から放射された音をダクトやカバー等の案内手段で絞りながら案内し、放射口を音源Ｐに近付けることによって距離ｄを小さくすることが有効である。
【００３０】
【実施例】
以下、図面を参照しながら実施例を説明する。
【００３１】
図５には本発明の第１の実施例に係る能動消音装置が示されている。
【００３２】
この能動消音装置は、適応制御方式を採用したもので、筐体２１内の制御対象機器２２の騒音と相関のある信号を検出して制御系への入力信号とするセンシング部２３と、制御系の制御係数を時々刻々適応的に算出する制御係数算出部（Ａ−ＦＩＲ）２４と、算出された制御係数と入力信号との積和演算を行いその結果を出力する制御係数積和演算部（ＦＩＲ）２５と、筐体２１の開口部２９を挟むように筐体外に配置され制御係数積和演算部２５の出力を入力信号として開口部２９から外部にむけて３次元的に放射される騒音と干渉する音を発生する２つのスピーカからなる付加音源２６ａ，２６ｂと、開口部２９から放射される音と付加音源２６ａ，２６ｂから放射される音との和を検出して誤差信号とみなす誤差信号検出器としての評価用マイク２７とから構成されている。この例では、制御係数演算部２４と制御積和演算部２５とで制御系２８が構成されている。
【００３３】
図５に示す装置では、評価用マイク２７と、音源と見なされる開口部２９（以後、音源２９と呼ぶ場合もある）の中心と、各付加音源２６ａ，２６ｂの振動面とが音源２９の振動面前方に描かれる正三角形の頂点に位置するように設定されている。そして、評価用マイク２７の出力が最小となるように制御系２８で各付加音源２６ａ，２６ｂが制御される。
【００３４】
各構成部材をこのような配置にすると、（６） 式および（７） 式から音源２９に対する付加音源２６ａ，２６ｂの位相が１８０度、体積速度比が１／２に近づき、音源２９から涌き出した流体と同じ量だけ付加音源２６ａ，２６ｂで吸い込ませることができ、音源２９から３次元的に放射される音響パワ―そのものを最小に抑えることができる。
【００３５】
なお、図６に示す第２の実施例のように、機器２２を開放空間に置くときは、開口部２９の代わりに機器２２の振動面が位置するように配置することによって図５の場合と同様の効果を得ることができる。図５および図６において、上述した条件を満たせば、付加音源は２個に限られるものではない。
【００３６】
次に、図７を参照して第３の実施例について説明する。
【００３７】
この第３の実施例に係る装置では、付加音源２６ａ，２６ｂの振動面を筐体２１の開口部２９の両側で、開口部２９と同じ面上に位置させている。そして、評価用マイク２７を２つの付加音源２６ａ，２６ｂの振動面から等距離に、かつ騒音と相関のある信号を検出できる範囲で音源である開口部２９からできるだけ離れた位置に配置している。
【００３８】
各構成部材をこのような配置にすると、評価用マイク２７を開口部２９、つまり音源２９から離せば離すほど、図２および図３を用いて説明した（ｈ_１ −ｈ_２ ）、（ｈ_１ −ｈ_３ ）の差がなくなり、（６） 式および（７） 式から判るように、音源２９に対して付加音源２６ａ，２６ｂの位相が１８０度ずれるので、前記実施例と同様に全音響パワーを低減できる。
【００３９】
なお、図８に示す第４の実施例のように、機器２２を開放空間に置くときは、筐体の開口部２９の代わりに機器２２の振動面が位置するように配置すれば上記装置の場合と同様の効果を得ることができる。
【００４０】
また、図９に示す第５の実施例のように、一方の付加音源２６ａには制御係数算出部２４ａおよび制御係数積和演算部２５ａの回路を接続し、他方の付加音源２６ｂには制御係数算出部２４ｂおよび制御係数積和演算部２５ｂの回路を接続し、このような制御系２８により各付加音源２６ａ，２６ｂをそれぞれ別個独立に制御するようにしてもよい。
【００４１】
また、図１０に示す第６の実施例のように、付加音源２６ｂと筐体２１の開口部２９との間に評価用マイク２７を配置してもよい。特に、評価用マイク２７を配置する位置は、図１１に示すパワー分布図のうちパワーの最も低いマイナス１０ｄＢの等高線が横軸と交わる位置が最適である。
【００４２】
この最適位置は、発明者らの検討によると付加音源までの距離をｄとした場合に、約０．６ｄだけ離れた位置が該当する。なお、図１１に示す例は、音源である開口部２９から付加音源２６ａ，２６ｂまでの距離ｄが０．３ ｍの場合であり、評価用マイク２７の最適位置は０．１８ｍ（＝０．３ ｍ×０．６ ）となる。したがって、評価用マイク２７を一方の付加音源２６ｂ（２６ａ）と音源２９との間に設ける場合は、音源２９から０．１８ｍ離れた付近に評価用マイク２７を配置するのがよい。
【００４３】
このように評価用マイク２７を付加音源２６ａ，２６ｂの振動面および音源２９（筐体の開口部）の振動面と同一面内に設けても同様に能動消音することができる。
【００４４】
図１１および図１２を参照しながら、上記配置の装置であっても能動消音することが可能になる理由について説明する。
【００４５】
図１１および図１２は、横軸および縦軸に音の放射源からの距離をそれぞれとり、図１１では図５，図７，図１０に示す同期制御タイプ装置のパワー分布特性を示し、図１２では図１０に示す独立制御タイプ装置のパワー分布特性を示す。すなわち、図１１および図１２は、上記各タイプの装置において、周波数２００Ｈｚ の条件下での音響パワー低下量をそれぞれ測定し、その結果のパワー変化量等高線を２ｄＢ の間隔で表示したものである。
【００４６】
両図から明らかなように、音源２９から評価用マイク２７を離せば離すほどパワーが減少し、消音効果が増す。また、図１１から明らかなように、付加音源２６ｂの振動面と音源２９の振動面とで挟まれた領域においても−１０ｄＢ〜０ｄＢ となる部分が存在し、図１０に示すような評価用マイクの置きかたによって消音効果を得ることができる。
【００４７】
一方、図１２から明らかなように、付加音源２６ｂの振動面と音源２９の振動面とで挟まれた領域には０ｄＢ 以下となる部分が存在しないので、図１０に示すような評価用マイク２７の置きかたによって消音効果を得ることはできない。したがって、図１０に示す配置の装置は、同期制御の場合にのみに消音可能であり、独立制御の場合には消音することができない。
【００４８】
図１３には本発明の第７の実施例に係る能動消音装置が示されている。
【００４９】
なお、この図では図５と同一部分が同一符号で示してある。したがって、重複する部分の詳しい説明は省略する。
【００５０】
この実施例は、機器２２で発生した騒音がダクト３０の開口部３１から３次元的に放射される系を対象にし、開口部３１から放射される音響パワーを低減させる例である。したがって、この系では結果的に開口部３１が音源となるので、以後の説明では開口部３１を音源と呼ぶ場合もある。
【００５１】
先に図５〜図９を用いて説明した例では、音源３１の両側に付加音源２６ａ，２６ｂを配置し、音源３１の振動面の前方に評価用マイク２７を配置しているが、この例では、図１４にも示すように音源３１の振動面の延長面上に付加音源２６ａ，２６ｂの振動面および評価用マイク２７を位置させている。
【００５２】
そして、この例においては、図１４に示すように、ダクト３０の半径方向外側で、評価用マイク２７の中心と、音源３１（ダクト出口）の振動面の中心３２と、各付加音源２６ａ，２６ｂの振動面の中心とが正三角形の頂点にそれぞれ位置するように関係づけられている。
【００５３】
各構成部材をこのような配置にすると、図５の例と同様に、音源３１（ダクト出口）から湧き出した流体と同じ量だけ付加音源２６ａ，２６ｂで吸い込ませることができ、音源３１から放射される騒音の音響パワ―を最小にできる。
【００５４】
この配置における消音効果を図１５を用いて説明する。
【００５５】
図１５（ａ） は音源３１と付加音源２６ａ，２６ｂと間の距離をｄ＝０．３ ｍに固定した状態で、評価用マイク２７の位置による音響パワ―の低下量と周波数の関係を示している。図１５（ａ） の横軸は評価用マイク２７の位置を表す。音源３１を原点にとり、単位はメ―トルである。ダクト出口によって構成される音源３１はモノポ―ル音源となることから、ダクト出口の中心３２が原点となる。また、縦軸は周波数を表す。そして、図中の等高線の数値は音響パワ―の低下量を示す。
【００５６】
この図１５（ａ） から判るように、音源から０．３ ｍ離れた位置でパワ―が最も低下している。ちなみに、計算よるとこの場合、１０Ｈｚで約４０ｄＢ，５０Ｈｚで約２２ｄＢ，１００Ｈｚ で約１７ｄＢ，２００Ｈｚ で約１０ｄＢの低減効果がある。評価用マイク２７を音源と付加音源２６ａ，２６ｂとの間の距離ｄ以上離して設置した場合では、１０〜４０Ｈｚ程度の低周波では良好な消音効果が得られないが、５０Ｈｚでは約１５ｄＢもの効果が得られることが判る。
【００５７】
音源と付加音源との間の距離ｄを小さくするほど消音効果が向上する。
【００５８】
図１６（ａ） にはｄ＝０．１６ｍのときの音響パワ―の低下量分布を示す。
【００５９】
この図から、評価用マイク２７と音源３１（ダクト出口）と各付加音源２６ａ，２６ｂの振動面とを正三角形の頂点にそれぞれ配置する構成では、ｄを小さくするほど、４０Ｈｚ以下の低周波から７００Ｈｚ 程度の高周波域まで音響パワーを低下させることができ、消音可能な周波数範囲を広げることが可能となる。
【００６０】
なお、図１７に示す第８の実施例のように、付加音源２６ａ，２６ｂを音源３１（ダクト出口）の両側に配置し、評価用マイク２７を２つの付加音源２６ａ，２６ｂの振動面から等距離に置き、かつ騒音と相関のある信号を検出できる範囲で、音源３１からできるだけ離すように設置すると、図７および図８に示した例と同様に、図２および図３を用いて説明した（ｈ_１ −ｈ_２ ）、（ｈ_１ −ｈ_３ ）の差がなくなり、（６） 式および（７） 式から判るように、音源３１に対して付加音源２６ａ，２６ｂの位相が１８０度ずれ、体積速度比が１／２に近づくので、ダクト出口から放射される騒音の全音響パワーを低減できる。この場合も、音源３１と付加音源２６ａ，２６ｂとの間の距離ｄを小さくするほど効果が大きくなる。
【００６１】
上記のように音源３１と付加音源２６ａ，２６ｂとの間の距離ｄを小さくするほど大きな効果が得られるが、たとえばタービンの排ガス路のようなダクト構成の場合には、ダクトが高温であるため付加音源２６ａ，２６ｂをダクトに近付けることができない。また、付加音源２６ａ，２６ｂの寸法が大きい場合も同様なことがいえる。
【００６２】
図１８および図１９には上述した問題を解決した第９の実施例が示されている。
【００６３】
これらの図では図１３と同一部分が同一符号で示されている。したがって、重複する部分の説明は省略する。
【００６４】
この例では、付加音源２６ａ，２６ｂから放射された音を案内路を構成するカバー部材３３ａ，３３ｂで絞り、この絞られた音をダクト出口３１に近接した位置から放射させるようにしている。
【００６５】
したがって、カバー部材３３ａ，３３ｂを設けることによって、付加音源２６ａ，２６ｂの振動面中心位置３４から音源３１の中心３２までの距離ｄ_１ に比べて、実際の放射面中心位置３５から音源３１の中心３２までの距離ｄ_２ （ｄ_２ ＜ｄ_１ ）を短くすることが可能となり、付加音源の大きさを変更させることなしに、またダクト３０が高温の場合であっても、良好な消音効果を得ることが可能となる。
【００６６】
図２０および図２１には、本発明の第１０の実施例に係る能動消音装置が示されている。
【００６７】
これらの図では図１３と同一部分が同一符号で示されている。したがって、重複する部分の説明は省略する。
【００６８】
この実施例ではダクト３０の半径方向外側で、音源３１（ダクト出口）の振動面を通る線上に、音源３１を挟むように付加音源２６ａ，２６ｂを配置するとともに、上記線上に評価用マイク２７を配置している。この例では、特に音源３１の中心３２と付加音源２６ａ、２６ｂとの間の距離をｄとしたとき、音源３１の中心３２からｘ＝０．６ｄだけ離れた位置に評価用マイク２７を配置している。
【００６９】
この配置における消音効果を図２２，図２３により説明する。
【００７０】
図２２は音源３１の中心３２と付加音源２６ａ，２６ｂとの間の距離を０．２２ｍに固定させた状態での評価用マイク２７の位置による音響パワ―の低下量と周波数との関係を示す。図２３は横軸が評価用マイクの位置を示し、縦軸が周波数を示している。音源３１の中心３２（ダクト出口の中心）を原点にとっている。そして、図中の等高線の数値は音響パワ―の低下量を示す。
【００７１】
評価用マイク２７の設置範囲を付加音源２６ａの内側（Ｘ＜ｄ：但し、Ｘは音源中心から評価用マイクまでの距離）とした場合、この範囲では図２４に示すように評価用マイク位置のわずかな違いにより位相、体積速度の変化が大きくなることから、位相が１８０度に、体積速度比が１／２に近づく状態は得られにくく、音響パワ―の変化も大きくなる。したがって、音響パワ―を大幅に低下させるための評価用マイク設置範囲はＸ／ｄ＝０．６ （０．１３ｍ）と狭くなる。しかし、うまくこの位置に評価用マイクを設置できれば、高周波帯域（Ｃ／２ｄ）Ｈｚまで消音が可能となる。ちなみに、１００Ｈｚ では約２２ｄＢ低下する。
【００７２】
これに対して図２８に示すように、評価用マイク設置範囲を付加音源２６ａより外側（Ｘ＞ｄ）とした場合、消音周波数は低周波帯域に限られるが、図２４に示すように評価用マイク２７を音源から離すほど、付加音源の位相が１８０度に、また図２５に示すように体積速度比が１／２に近づくことから音響パワ―が低下し、位相、体積速度の変化量もゆるやかであることから、安定した消音効果が得られ、評価用マイク２７の設置範囲を広くできることになる。
【００７３】
図２６および図２７は音源（ダクト出口）から付加音源までの距離ｄを変えたときの評価用マイク位置の違いによる音響パワ―低下量の計算結果（音響パワ―が増加する領域は示していない。）であるが、ｄが小さくなるとパワ―低下量が大きくなり消音する周波数範囲も広がり、消音効果が向上することが判る。
【００７４】
そこで、図１８の場合と同様に、図２９および図３０に示す第１１の実施例のように、付加音源２６ａ，２６ｂの周囲に案内路を構成するカバ―部材３３ａ，３３ｂを設置することにより、付加音源２６ａ，２６ｂの放射面中心３４をカバ―部材３３ａ，３３ｂの出口３５に変えることにより、音源３１（ダクト出口）から付加音源放射面中心までの距離を短くすることが可能となり、消音効果をより向上させることが可能となる。
【００７５】
図３１および図３２には、図２９および図３０に示す能動消音装置についての消音効果の実測例が示されている。
【００７６】
実験に用いたダクトは内径２５０ ｍｍ、長さ１５６０ｍｍである。ダクトの最奥部に設置された音源用スピ―カからランダム音（〜１ｋＨｚ）を出力し、ダクト出口から３次元空間に放射される音に対して能動消音を実施した。ダクト出口をモノポ―ル音源の中心と仮定し、ダクト出口から半径方向両側にｄ＝０．２２ｍ（ｄ＝０．３ ｍ）離れた位置に付加音源であるアクティブスピ―カをそれぞれ設置し、Ｆｉｌｔｅｒｅｄ−Ｘアルゴリズの適応制御を行った。消音効果は評価用マイクの音圧が十分に低下した後に、周囲に設置したモニタマイクの平均音圧レベル差で評価した。最適配置で効果があることを確認するため、評価用マイクをダクト出口とアクティブスピ―カを結ぶ線上に移動させ、制御前後の低減効果を測定した。
【００７７】
図３１はダクト出口から付加音源までの距離ｄが０．２２ｍの場合、図３２は距離ｄが０．３ ｍの場合である。両者を比較すると最適配置（Ｘ／ｄ＝０．６ ）では距離ｄが小さいほうが、音圧の低下量も大きく、高い周波数まで低下していることが判る。１００ 〜５００ Ｈｚバンドの結果で比較するとｄ＝０．２２ｍのときは約６ｄＢ 、ｄ＝０．３ ｍのときは約３ｄＢ 低下した。
【００７８】
一方、評価用マイク２７をアクティブスピ―カの外側（Ｘ＞ｄ）に設置したときも同様に、計算上低下する１００ 〜２００Ｈｚ バンドの低周波帯域（〜２００Ｈｚ ）では実測値も低下しており、ｄ＝０．２２ｍの方が低下量も大きい結果を得た。
【００７９】
これにより、ここに提案した能動消音装置の有効性を確認するとともに、ダクト出口から付加音源の放射面までの距離ｄを小さくすることで、消音効果を向上させることができることを確認できた。
【００８０】
なお、上述した各実施例では、付加音源を２個用いているが、１つの音源に対して付加音源を２個以上のＮ個用い、１本の評価用マイクで適応制御を行うときにおいても本手法は有効である。
【００８１】
すなわち、図１に示したように、音源Ｐの吹出し体積速度をＡとすると、音源Ｐに対して１８０度（逆相）で、かつ吸い込み体積速度がＡ／Ｎとなるようにそれぞれの付加音源を制御すれば、音源Ｐから吹出した流体と同じ量だけＮ個の付加音源で吸い込むことができ、音響パワーを最小にすることができる。
【００８２】
Ａ＝Ｎ・Ａ／Ｎ （Ｎ＝１，２，３，…）
１つの音源に対してＮ個の付加音源を付加することで、全体の音響パワーは、（１） 式のようになる。また、音源ｉの体積速度Ａｉは（２） 式のようになり、１本の評価用マイクで音源の合成音を検出し、この評価用マイクでの音圧を最小にするように制御を行い、付加音源の吸い込み体積速度と位相を変化させる。
【００８３】
制御後の体積速度と位相は、（３） 式〜（５） 式で示され、音響パワーを低減させるには評価用マイク、付加音源等の配置が重要となる。
【００８４】
（３） 式〜（５） 式から、評価用マイクおよび付加音源の配置の仕方により、適応制御後の付加音源の位相と体積速度とが決められるので、（１） 式にそれぞれの位相、体積速度を代入することで、この配置における全音響パワーが決定される。言いかえると、全音響パワーは評価用マイクおよび付加音源の位置の関数になることから、これらの設置方法をかえることで、全音響パワーをコントロールできることになる。
【００８５】
この原理に基づき、Ｎ個の付加音源の位相が１８０度で、かつＡ／Ｎの吸い込み体積速度になるように評価用マイクおよび付加音源を配置することで、適応制御により騒音源の音響パワーを最小にでき、周囲全体を消音することが可能となる。
【００８６】
なお、騒音源に対して位相が逆相で、かつＡ／Ｎの吸い込み体積速度となるように個々の付加音源を配置しなくても、騒音源の吹出し体積速度Ａに対して付加音源の吸い込み体積速度の総和がＡとなるように評価用マイクおよび付加音源を配置することで、騒音源の音響パワーを最小にできる。
【００８７】
【発明の効果】
以上の説明したように、本発明によれば評価マイクの位置で音圧を零にするように決定された制御係数で同時に音源の音響パワーを最小にする制御が可能となり、音源から３次元的に伝播しようとする音響パワーそのものをアクティブに低減できる。
【図面の簡単な説明】
【図１】本発明装置の原理を説明するため図
【図２】本発明装置の原理を説明するため図
【図３】本発明装置の原理を説明するため図
【図４】本発明装置の原理を説明するため図
【図５】本発明の第１の実施例に係る能動消音装置のブロック構成図
【図６】本発明の第２の実施例に係る能動消音装置のブロック構成図
【図７】本発明の第３の実施例に係る能動消音装置のブロック構成図
【図８】本発明の第４の実施例に係る能動消音装置のブロック構成図
【図９】本発明の第５の実施例に係る能動消音装置のブロック構成図
【図１０】本発明の第６の実施例に係る能動消音装置のブロック構成図
【図１１】音の放射源を原点にとって近傍領域における音響パワーの分布状態を示すパワー分布特性図
【図１２】音の放射源を原点にとって近傍領域における音響パワーの分布状態を示すパワー分布特性図
【図１３】本発明の第７の実施例に係る能動消音装置のブロック構成図
【図１４】図１３においてＨ−Ｈ線に沿って矢印方向に見た概略図
【図１５】同実施例においてｄ＝０．３ ｍに設定したときの評価用マイク位置の違いによる消音効果の違いを示す図
【図１６】同実施例においてｄ＝０．１６ｍに設定したときの評価用マイク位置の違いによる消音効果の違いを示す図
【図１７】本発明の第８の実施例に係る能動消音装置の要部配置図
【図１８】本発明の第９の実施例に係る能動消音装置のブロック構成図
【図１９】図１８においてＩ−Ｉ線に沿って矢印方向に見た概略図
【図２０】本発明の第１０の実施例に係る能動消音装置のブロック構成図
【図２１】図２０においてＪ−Ｊ線に沿って矢印方向に見た概略図
【図２２】同実施例において評価用マイク位置の違いによる消音効果の違いを示す図
【図２３】同実施例において評価用マイク位置の違いによる消音効果の違いを示す図
【図２４】同実施例において評価用マイク位置の違いによる音源に対する位相特性を示す図
【図２５】同実施例において評価用マイク位置の違いによる体積速度比特性を示す図
【図２６】同実施例においてｄ＝０．２２ｍに設定したときの評価用マイク位置の違いによる消音効果の違いを示す図
【図２７】同実施例においてｄ＝０．３ ｍに設定したときの評価用マイク位置の違いによる消音効果の違いを示す図
【図２８】本発明の第１１の実施例に係る能動消音装置の要部配置図
【図２９】本発明の第１２の実施例に係る能動消音装置のブロック構成図
【図３０】図２９においてＫ−Ｋ線に沿って矢印方向に見た概略図
【図３１】図２０および図２８に示す装置の評価用マイク位置の違いによる消音効果の実測値を示す図
【図３２】図２０および図２８に示す装置の評価用マイク位置の違いによる消音効果の実測値を示す図
【図３３】従来のパッシブな消音処理の説明図
【図３４】従来の能動消音装置の一例を示す図
【図３５】従来の能動消音装置の別の例を示すブロック構成図
【図３６】従来の能動消音装置における不具合例の説明図
【符号の説明】
２１…制御対象機器 ２２…センシング部
２３…制御係数算出部 ２４…制御係数積和演算部（Ａ−ＦＩＲ）
２５…付加音源部（ＦＩＲ） ２６ａ，２６ｂ…付加音源
２７…音検出手段としての評価用マイク ２８…制御系
３０…ダクト ３１…ダクト開口部（音源）
３２…音源の中心 ３３ａ，３３ｂ…カバー部材[0001]
[Industrial application fields]
The present invention relates to an active silencer that can actively reduce the acoustic power itself that is about to propagate three-dimensionally from a sound source.
[0002]
[Prior art]
The noise radiated from the openings of various devices and ducts often deteriorates the living environment and workplace environment. For this reason, various noise reduction measures are taken.
[0003]
Most commonly, as shown in FIG. 33, a passive method is adopted in which a device 8 that generates noise is housed in the housing 4 and the opening of the housing 4 is covered with a sound insulating material 5. . However, in this method, there is a problem of how the heat generated in the device 8 is discharged to the outside.
[0004]
For this reason, an active method has recently been adopted as shown in FIG. That is, in this method, the peaker 9 as an additional sound source is installed in the opening of the housing 4 and the evaluation microphone 10 is provided, and the speaker 9 is controlled so that the noise in the vicinity of the evaluation microphone 10 is minimized. Yes.
[0005]
On the other hand, an active silencer as shown in FIG. 35 is known as a system for silencing noise radiated from the opening of a duct by an active method.
[0006]
That is, in the case of the air-conditioning duct 6 and the like, the sound is often propagated one-dimensionally. Set the pressure to zero. When a point with zero sound pressure is created, the sound is reflected at that point due to the difference in acoustic impedance and does not propagate to the opening side. Whether or not a point of zero sound pressure has been formed is evaluated by an evaluation microphone 10 installed downstream of the speaker 9. That is, the control coefficient of the mute controller 11 is determined so that the sound pressure becomes zero at the installation position of the evaluation microphone 10. Note that the detection microphone 12 is used to detect the sound generated by the sound source 8.
[0007]
The method of automatically determining the control coefficient so that the sound pressure approaches zero is called an “adaptive control system”, and is often used in an active silencing system for a duct structure in which sound propagates one-dimensionally. Thus, when sound propagates one-dimensionally, if the sound is reflected by creating a point with zero sound pressure, the object can be achieved without propagating downstream.
[0008]
By the way, in the active silencer shown in FIGS. 34 and 35, it is necessary to attach a speaker and an evaluation microphone to the inside of the casing or the duct. However, a speaker or an evaluation microphone cannot be mounted inside an existing facility or an exhaust duct of a gas turbine that is subjected to severe thermal conditions.
[0009]
Therefore, for such equipment, for example, it is conceivable to perform active silencing by attaching a speaker or an evaluation microphone outside the opening of the exhaust duct.
[0010]
However, in this case, the sound to be muffled is not a sound that propagates one-dimensionally, but a sound that propagates three-dimensionally to an open space using the opening as a sound source. For this reason, making the sound zero at the position of the evaluation microphone does not necessarily reduce the overall noise. For example, assume that an evaluation score 13 is set as shown in FIG. Even if the control coefficient is determined so that the sound pressure is made zero at the evaluation point 13, the sound pressure cannot be made zero at locations other than the evaluation point, so that the overall sound power cannot be minimized.
[0011]
As described above, in the conventional active silencer, there is a problem that the sound that is three-dimensionally propagated from the sound source can be silenced only locally, and the noise cannot be reduced over the whole.
[0012]
[Problems to be solved by the invention]
As described above, in the conventional active silencer, a good silencing effect can be obtained under the condition that the sound is propagated one-dimensionally. There was a problem that could not be done.
[0013]
Accordingly, an object of the present invention is to provide an active silencer that can actively reduce the acoustic power itself that is about to propagate three-dimensionally from a sound source.
[0014]
[Means for Solving the Problems]
In order to achieve the above object, in an active silencer according to an example of the present invention, a plurality of additional sound sources for radiating sound that interferes with sound radiated three-dimensionally from a sound source, and radiation from the sound source. Sound detection means provided in a space through which the transmitted sound is transmitted, and control means for controlling each additional sound source to minimize the output of the sound detection means, each additional sound source and the sound detection means, The sound source, the additional sound source, and the sound detection means are arranged at respective vertices of an equilateral triangle.
[0015]
[Action]
In the active silencer according to an example of the present invention, a plurality of, for example, two additional sound sources are provided, and consideration is given to the relative positions of these additional sound sources, sound detection means, and sound sources.
[0016]
Now, as shown in FIG. 1, N additional sound sources S for one sound source P₁, S₂, ... S_NConsider reducing the overall acoustic power by adding.
[0017]
All sound power after addition W_allIs as follows.
[0018]
[Expression 1]

However, the N + 1 sound sources are all breathing spheres in the field of acoustics, that is, monopole sound sources. (1) In the formula, R_ijIs radiation resistance, V_i, Θ_iRepresents the vibration speed and phase of the sound source i.
[0019]
The sound intensity of the sound source i, that is, the volume velocity is A_iThen,
A_i= 4 πr_i ²｜ V_i| (R_i: Vibration radius) (2)
Therefore, all sound power W_allIt can be seen that changes depending on the volume velocity (amplitude) and phase of each sound source.
[0020]
Therefore, the sound detection means (evaluation microphone) installed in the space detects the synthesized sound of the sound source, performs control to minimize the sound pressure at this sound detection means, and the volume velocity and phase of each additional sound source To change.
[0021]
Since the volume velocity and phase after the control are determined by the following equations (3), (4), and (5), as shown in FIG. 2, the acoustic power of the entire periphery of the sound source P is reduced. Is sound detection means M and each additional sound source S₁, S₂, ... S_NIt can be seen that the arrangement of is important.
[0022]
[Expression 2]

Where ρ: air density, ω: angular frequency, h_i: Distance from i-th additional sound source to sound detection means M, k: wave number, θ_i: I-th additional sound source phase, θ₁: The phase of the sound source P.
[0023]
Therefore, as shown in FIG. 3, the two additional sound sources S₁, S₂Let's think about the case of providing.
[0024]
Now, two additional sound sources S₁, S₂Are in phase and are arranged equidistant from the sound source P, the additional sound source S relative to the sound source P₁, S₂The phase θ and the volume velocity ratio α (A2 / A1) are expressed by the following equations.
[0025]
[Equation 3]

Therefore, the acoustic power decrease amount η (dB) after control is expressed by the following equation.
[0026]
[Expression 4]

In the active silencer according to one example of the present invention, for example, as shown in FIG.₁, S₂Since the sound detection means M are arranged so as to be located, when the above-described control is performed, the additional sound source S for the sound source P is obtained from the equations (6) and (7).₁, S₂The phase of the additional sound source S is 180 degrees, the volume velocity ratio approaches 1/2, and the amount of the additional sound source S is the same as the fluid spouted from the sound source P.₁, S₂The sound power radiated from the sound source P itself can be minimized.
[0027]
As shown in FIG. 4B, the additional sound source S is provided on both sides of the sound source P.₁, S₂, And a sufficient distance from the sound source P and the additional sound source S₁, S₂Distance h from the sound source P to the sound detection means M₁And additional sound source S₁, S₂Distance h from sound detection means M₂, H₃Since the difference between and (0) approaches zero, (h) in (6) and (7)₁-H₂) And (h₁-H₃) Term can be brought close to zero. Therefore, in this case as well, if the above-described control is performed, the additional sound source S with respect to the sound source P will be described.₁, S₂The phase of the additional sound source S is 180 degrees, the volume velocity ratio approaches 1/2, and the amount of the additional sound source S is the same as the fluid spouted from the sound source P.₁, S₂The sound power radiated from the sound source P can be sufficiently reduced.
[0028]
Further, according to experiments, as shown in FIG. 4C, the additional sound source S is separated from the sound source P by a distance d on a line passing through the sound source P on both sides of the sound source P.₁, S₂And the sound radiated from the sound source P even if the above-described control is performed by arranging the sound detection means M at the position of x = 0.6 d away from the sound source P on the same line or at the position of x> d. Power itself can be reduced.
[0029]
4A, 4B, and 4C, as will be described later, the sound source P and the additional sound source S are used.₁, S₂The smaller the distance d between the two, the more effective. Therefore, the additional sound source S₁, S₂Additional sound source S due to large heat or heat₁, S₂Cannot be brought close to the sound source P, the additional sound source S₁, S₂It is effective to reduce the distance d by guiding the sound radiated from the sound source with a guide means such as a duct or a cover, and bringing the radiation port close to the sound source P.
[0030]
【Example】
Hereinafter, embodiments will be described with reference to the drawings.
[0031]
FIG. 5 shows an active silencer according to the first embodiment of the present invention.
[0032]
This active silencer employs an adaptive control method, and includes a sensing unit 23 that detects a signal correlated with the noise of the control target device 22 in the casing 21 and uses it as an input signal to the control system, and a control system A control coefficient calculation unit (A-FIR) 24 that adaptively calculates the control coefficient of each time, and a control coefficient product-sum calculation unit that performs a product-sum operation of the calculated control coefficient and the input signal and outputs the result ( FIR) 25 and noise radiated three-dimensionally from the opening 29 to the outside using the output of the control coefficient product-sum operation unit 25 as an input signal, with the opening 29 of the housing 21 being sandwiched therebetween Error that is detected as an error signal by detecting the sum of the additional sound sources 26a and 26b composed of two speakers that generate sound that interferes with the sound, and the sound emitted from the opening 29 and the sound emitted from the additional sound sources 26a and 26b Reputation as a signal detector And a use microphone 27.. In this example, a control system 28 is configured by the control coefficient calculation unit 24 and the control product-sum calculation unit 25.
[0033]
In the apparatus shown in FIG. 5, the evaluation microphone 27, the center of an opening 29 (hereinafter also referred to as the sound source 29) regarded as a sound source, and the vibration surfaces of the additional sound sources 26 a and 26 b are vibrations of the sound source 29. It is set to be located at the apex of an equilateral triangle drawn in front of the surface. The additional sound sources 26a and 26b are controlled by the control system 28 so that the output of the evaluation microphone 27 is minimized.
[0034]
If each component is arranged in such a manner, the phase of the additional sound sources 26a and 26b with respect to the sound source 29 is 180 degrees and the volume velocity ratio is close to 1/2 according to the expressions (6) and (7). The additional sound sources 26a and 26b can be sucked by the same amount as the fluid, and the acoustic power radiated three-dimensionally from the sound source 29 can be minimized.
[0035]
When the device 22 is placed in an open space as in the second embodiment shown in FIG. 6, the device 22 is arranged so that the vibration surface of the device 22 is positioned instead of the opening 29. Similar effects can be obtained. 5 and 6, the additional sound source is not limited to two as long as the above-described conditions are satisfied.
[0036]
Next, a third embodiment will be described with reference to FIG.
[0037]
In the apparatus according to the third embodiment, the vibration surfaces of the additional sound sources 26 a and 26 b are positioned on the same surface as the opening 29 on both sides of the opening 29 of the housing 21. The evaluation microphone 27 is arranged at the same distance from the vibration surfaces of the two additional sound sources 26a and 26b and at a position as far as possible from the opening 29 as a sound source within a range in which a signal correlated with noise can be detected. .
[0038]
When the constituent members are arranged in this way, the evaluation microphone 27 is described with reference to FIGS. 2 and 3 as the evaluation microphone 27 is further away from the opening 29, that is, the sound source 29 (h).₁-H₂), (H₁-H₃) And the phases of the additional sound sources 26a and 26b are shifted by 180 degrees with respect to the sound source 29, as can be seen from the equations (6) and (7), so that the total sound power can be reduced as in the above embodiment. .
[0039]
When the device 22 is placed in an open space as in the fourth embodiment shown in FIG. 8, the device 22 can be placed so that the vibration surface of the device 22 is positioned instead of the opening 29 of the housing. The same effect as the case can be obtained.
[0040]
Further, as in the fifth embodiment shown in FIG. 9, one additional sound source 26a is connected to a circuit of a control coefficient calculation unit 24a and a control coefficient product-sum operation unit 25a, and the other additional sound source 26b is connected to a control coefficient. The circuits of the calculation unit 24b and the control coefficient product-sum operation unit 25b may be connected, and the additional sound sources 26a and 26b may be controlled independently by the control system 28.
[0041]
Further, as in the sixth embodiment shown in FIG. 10, the evaluation microphone 27 may be disposed between the additional sound source 26 b and the opening 29 of the housing 21. In particular, the position at which the evaluation microphone 27 is arranged is optimal at a position where the contour line of minus 10 dB having the lowest power intersects the horizontal axis in the power distribution diagram shown in FIG.
[0042]
According to the study by the inventors, this optimum position corresponds to a position separated by about 0.6 d, where d is the distance to the additional sound source. In the example shown in FIG. 11, the distance d from the opening 29, which is a sound source, to the additional sound sources 26a, 26b is 0.3 m, and the optimum position of the evaluation microphone 27 is 0.18 m (= 0.0 m). 3 m × 0.6). Therefore, when the evaluation microphone 27 is provided between the one additional sound source 26 b (26 a) and the sound source 29, the evaluation microphone 27 is preferably arranged near the sound source 29 by 0.18 m.
[0043]
As described above, even when the evaluation microphone 27 is provided in the same plane as the vibration surface of the additional sound sources 26a and 26b and the vibration surface of the sound source 29 (opening of the housing), the active mute can be similarly performed.
[0044]
With reference to FIG. 11 and FIG. 12, the reason why the apparatus having the above arrangement can be actively silenced will be described.
[0045]
11 and 12 show the distance from the sound radiation source on the horizontal axis and the vertical axis, respectively, and FIG. 11 shows the power distribution characteristics of the synchronous control type device shown in FIGS. 5, 7, and 10. Then, the power distribution characteristic of the independent control type apparatus shown in FIG. 10 is shown. That is, FIG. 11 and FIG. 12 respectively show the amount of decrease in acoustic power under the condition of a frequency of 200 Hz in each of the above-mentioned types of devices, and display the resulting power change amount contour lines at intervals of 2 dB.
[0046]
As is clear from both figures, as the evaluation microphone 27 is separated from the sound source 29, the power decreases and the silencing effect increases. As is clear from FIG. 11, there is a portion of −10 dB to 0 dB even in a region sandwiched between the vibration surface of the additional sound source 26b and the vibration surface of the sound source 29, and the evaluation microphone as shown in FIG. It is possible to obtain a silencing effect depending on how it is placed.
[0047]
On the other hand, as is clear from FIG. 12, there is no portion of 0 dB or less in the region sandwiched between the vibration surface of the additional sound source 26b and the vibration surface of the sound source 29. Therefore, the evaluation microphone 27 as shown in FIG. It is not possible to obtain a silencing effect depending on the placement. Therefore, the apparatus having the arrangement shown in FIG. 10 can mute only in the case of synchronous control, and cannot mute in the case of independent control.
[0048]
FIG. 13 shows an active silencer according to a seventh embodiment of the present invention.
[0049]
In this figure, the same parts as those in FIG. 5 are denoted by the same reference numerals. Therefore, detailed description of overlapping parts is omitted.
[0050]
In this embodiment, a system in which noise generated in the device 22 is radiated three-dimensionally from the opening 31 of the duct 30 is an example in which the acoustic power radiated from the opening 31 is reduced. Therefore, in this system, the opening 31 is the sound source as a result, and hence the opening 31 may be called the sound source in the following description.
[0051]
In the example described above with reference to FIGS. 5 to 9, the additional sound sources 26 a and 26 b are disposed on both sides of the sound source 31, and the evaluation microphone 27 is disposed in front of the vibration surface of the sound source 31. As shown in FIG. 14, the vibration surfaces of the additional sound sources 26 a and 26 b and the evaluation microphone 27 are positioned on the extension surface of the vibration surface of the sound source 31.
[0052]
In this example, as shown in FIG. 14, outside the radial direction of the duct 30, the center of the evaluation microphone 27, the center 32 of the vibration surface of the sound source 31 (duct outlet), and the additional sound sources 26a and 26b. Are related to each other so that the center of the vibration plane is located at the apex of the equilateral triangle.
[0053]
When each component is arranged in this manner, the additional sound sources 26 a and 26 b can suck the same amount as the fluid that has flowed out from the sound source 31 (duct outlet) as in the example of FIG. The acoustic power of noise can be minimized.
[0054]
The silencing effect in this arrangement will be described with reference to FIG.
[0055]
FIG. 15 (a) shows the relationship between the amount of decrease in acoustic power due to the position of the evaluation microphone 27 and the frequency in a state where the distance between the sound source 31 and the additional sound sources 26a and 26b is fixed at d = 0.3 m. ing. The horizontal axis of FIG. 15A represents the position of the evaluation microphone 27. The sound source 31 is taken as the origin, and the unit is meter. Since the sound source 31 constituted by the duct outlet is a monopole sound source, the center 32 of the duct outlet is the origin. The vertical axis represents frequency. The contour lines in the figure indicate the amount of decrease in acoustic power.
[0056]
As can be seen from FIG. 15 (a), the power decreases most at a position 0.3 m away from the sound source. By the way, according to the calculation, there is a reduction effect of about 40 dB at 10 Hz, about 22 dB at 50 Hz, about 17 dB at 100 Hz, and about 10 dB at 200 Hz. When the evaluation microphone 27 is installed at a distance d or more between the sound source and the additional sound sources 26a and 26b, a good silencing effect cannot be obtained at a low frequency of about 10 to 40 Hz, but an effect of about 15 dB at 50 Hz. It can be seen that
[0057]
As the distance d between the sound source and the additional sound source is decreased, the silencing effect is improved.
[0058]
FIG. 16 (a) shows a decrease amount distribution of acoustic power when d = 0.16 m.
[0059]
From this figure, in the configuration in which the evaluation microphone 27, the sound source 31 (duct outlet), and the vibration surfaces of the additional sound sources 26a and 26b are respectively arranged at the vertices of an equilateral triangle, the lower d is, the lower the frequency is 40 Hz or less. The acoustic power can be reduced to a high frequency range of about 700 Hz, and the frequency range that can be silenced can be expanded.
[0060]
As in the eighth embodiment shown in FIG. 17, the additional sound sources 26a and 26b are arranged on both sides of the sound source 31 (duct outlet), and the evaluation microphone 27 is placed on the vibration surface of the two additional sound sources 26a and 26b. As shown in FIGS. 2 and 3, as in the example shown in FIGS. 7 and 8, when placed at a distance and installed as far as possible from the sound source 31 within a range in which a signal correlated with noise can be detected. (H₁-H₂), (H₁-H₃) And the phase of the additional sound sources 26a and 26b is shifted by 180 degrees with respect to the sound source 31 and the volume velocity ratio approaches 1/2, as can be seen from the equations (6) and (7). The total acoustic power of the noise radiated from can be reduced. Also in this case, the effect increases as the distance d between the sound source 31 and the additional sound sources 26a and 26b decreases.
[0061]
As described above, the smaller the distance d between the sound source 31 and the additional sound sources 26a and 26b, the greater the effect. However, in the case of a duct configuration such as an exhaust gas passage of a turbine, for example, the duct is hot. The additional sound sources 26a and 26b cannot be brought close to the duct. The same applies to the case where the additional sound sources 26a and 26b have large dimensions.
[0062]
FIGS. 18 and 19 show a ninth embodiment which solves the above-described problem.
[0063]
In these drawings, the same parts as those in FIG. 13 are denoted by the same reference numerals. Therefore, the description of the overlapping part is omitted.
[0064]
In this example, the sound radiated from the additional sound sources 26a and 26b is throttled by the cover members 33a and 33b constituting the guide path, and the squeezed sound is radiated from a position close to the duct outlet 31.
[0065]
Therefore, by providing the cover members 33a and 33b, the distance d from the vibration surface center position 34 of the additional sound sources 26a and 26b to the center 32 of the sound source 31 is provided.₁The distance d from the actual radiation plane center position 35 to the center 32 of the sound source 31 compared to₂(D₂<D₁) Can be shortened, and a good silencing effect can be obtained without changing the size of the additional sound source and even when the duct 30 is hot.
[0066]
20 and 21 show an active silencer according to a tenth embodiment of the present invention.
[0067]
In these drawings, the same parts as those in FIG. 13 are denoted by the same reference numerals. Therefore, the description of the overlapping part is omitted.
[0068]
In this embodiment, the additional sound sources 26a and 26b are arranged so as to sandwich the sound source 31 on the line passing through the vibration surface of the sound source 31 (duct outlet) outside the duct 30 in the radial direction, and the evaluation microphone 27 is placed on the line. It is arranged. In this example, particularly when the distance between the center 32 of the sound source 31 and the additional sound sources 26a and 26b is d, the evaluation microphone 27 is arranged at a position separated from the center 32 of the sound source 31 by x = 0.6d. ing.
[0069]
The silencing effect in this arrangement will be described with reference to FIGS.
[0070]
FIG. 22 shows the relationship between the amount of decrease in acoustic power due to the position of the evaluation microphone 27 and the frequency when the distance between the center 32 of the sound source 31 and the additional sound sources 26a and 26b is fixed to 0.22 m. . In FIG. 23, the horizontal axis indicates the position of the evaluation microphone, and the vertical axis indicates the frequency. The center 32 of the sound source 31 (the center of the duct outlet) is taken as the origin. The contour lines in the figure indicate the amount of decrease in acoustic power.
[0071]
When the installation range of the evaluation microphone 27 is set inside the additional sound source 26a (X <d: where X is the distance from the sound source center to the evaluation microphone), the range of the evaluation microphone position is as shown in FIG. Since the change in phase and volume velocity is increased by a slight difference, it is difficult to obtain a state in which the phase is 180 degrees and the volume velocity ratio is close to 1/2, and the change in acoustic power is also increased. Therefore, the evaluation microphone installation range for greatly reducing the acoustic power is narrowed to X / d = 0.6 (0.13 m). However, if the evaluation microphone can be successfully installed at this position, it is possible to mute up to the high frequency band (C / 2d) Hz. Incidentally, at 100 Hz, it is reduced by about 22 dB.
[0072]
On the other hand, as shown in FIG. 28, when the evaluation microphone installation range is outside the additional sound source 26a (X> d), the muffling frequency is limited to the low frequency band, but as shown in FIG. As the microphone 27 is moved away from the sound source, the phase of the additional sound source becomes 180 degrees, and the volume velocity ratio approaches 1/2 as shown in FIG. 25, so that the acoustic power decreases, and the amount of change in the phase and volume velocity also increases. Since it is gentle, a stable silencing effect can be obtained and the installation range of the evaluation microphone 27 can be widened.
[0073]
FIG. 26 and FIG. 27 show the calculation results of the amount of decrease in acoustic power due to the difference in the microphone position for evaluation when the distance d from the sound source (duct outlet) to the additional sound source is changed (the region where the acoustic power increases is not shown). However, it can be seen that as d decreases, the power reduction amount increases and the frequency range for silencing increases and the silencing effect improves.
[0074]
Therefore, as in the case of FIG. 18, as in the eleventh embodiment shown in FIGS. 29 and 30, cover members 33a and 33b constituting guide paths are provided around the additional sound sources 26a and 26b. By changing the radiation surface center 34 of the additional sound sources 26a, 26b to the outlet 35 of the cover members 33a, 33b, the distance from the sound source 31 (duct outlet) to the center of the additional sound source radiation surface can be shortened. The effect can be further improved.
[0075]
31 and 32 show actual measurement examples of the silencing effect for the active silencer shown in FIGS. 29 and 30. FIG.
[0076]
The duct used for the experiment has an inner diameter of 250 mm and a length of 1560 mm. A random sound (˜1 kHz) was output from a sound source speaker installed at the innermost part of the duct, and active muffling was performed on the sound radiated from the duct exit to the three-dimensional space. Assuming that the duct exit is the center of the monopole sound source, active speakers as additional sound sources are installed at positions d = 0.22 m (d = 0.3 m) on both sides in the radial direction from the duct exit, Adaptive control of the Filtered-X algorithm was performed. The silencing effect was evaluated by the difference in the average sound pressure level of the monitor microphones installed in the surroundings after the sound pressure of the evaluation microphone was sufficiently reduced. In order to confirm that the optimal placement was effective, the evaluation microphone was moved on the line connecting the duct outlet and the active speaker, and the reduction effect before and after the control was measured.
[0077]
FIG. 31 shows a case where the distance d from the duct outlet to the additional sound source is 0.22 m, and FIG. 32 shows a case where the distance d is 0.3 m. Comparing the two, it can be seen that in the optimum arrangement (X / d = 0.6), the smaller the distance d, the larger the amount of decrease in sound pressure, and the lower the frequency. Comparing the results in the band of 100 to 500 Hz, it was about 6 dB lower when d = 0.22 m and about 3 dB lower when d = 0.3 m.
[0078]
On the other hand, when the evaluation microphone 27 is installed outside the active speaker (X> d), the measured value also decreases in the low frequency band (up to 200 Hz) of the 100 to 200 Hz band, which is similarly reduced in calculation. D = 0.22 m gave a larger decrease.
[0079]
Thereby, while confirming the effectiveness of the active silencer proposed here, it was confirmed that the silencing effect could be improved by reducing the distance d from the duct outlet to the radiation surface of the additional sound source.
[0080]
In each of the embodiments described above, two additional sound sources are used. However, when two or more N additional sound sources are used for one sound source and adaptive control is performed with one evaluation microphone. This method is effective.
[0081]
That is, as shown in FIG. 1, when the volume velocity of the sound source P is A, each additional sound source is 180 degrees (reverse phase) with respect to the sound source P and the suction volume velocity is A / N. Can be sucked by the N additional sound sources by the same amount as the fluid blown from the sound source P, and the acoustic power can be minimized.
[0082]
A = N · A / N (N = 1, 2, 3, ...)
By adding N additional sound sources to one sound source, the overall sound power is expressed by equation (1). Further, the volume velocity Ai of the sound source i is expressed by the following equation (2), and the synthesized sound of the sound source is detected with one evaluation microphone, and control is performed so as to minimize the sound pressure with this evaluation microphone. The suction volume velocity and phase of the additional sound source are changed.
[0083]
The volume velocity and phase after the control are expressed by the equations (3) to (5), and the arrangement of the evaluation microphone, the additional sound source, etc. is important for reducing the acoustic power.
[0084]
(3) From Formula (5) to Formula (5), the phase and volume velocity of the additional sound source after adaptive control are determined depending on the arrangement of the evaluation microphone and the additional sound source. By substituting velocity, the total acoustic power in this arrangement is determined. In other words, since the total acoustic power is a function of the position of the evaluation microphone and the additional sound source, the total acoustic power can be controlled by changing these installation methods.
[0085]
Based on this principle, by arranging the evaluation microphone and the additional sound source so that the phase of the N additional sound sources is 180 degrees and the suction volume velocity is A / N, the acoustic power of the noise source is controlled by adaptive control. It can be minimized and the entire periphery can be silenced.
[0086]
It should be noted that the suction of the additional sound source with respect to the blowing volume velocity A of the noise source is not required even if the individual additional sound sources are arranged so that the phase is opposite to that of the noise source and the suction volume velocity is A / N. By arranging the evaluation microphone and the additional sound source so that the sum of the volume velocities becomes A, the acoustic power of the noise source can be minimized.
[0087]
【The invention's effect】
As described above, according to the present invention, it is possible to control the sound power of the sound source to be minimized simultaneously with the control coefficient determined to make the sound pressure zero at the position of the evaluation microphone. It is possible to actively reduce the sound power itself that is going to propagate to.
[Brief description of the drawings]
FIG. 1 is a diagram for explaining the principle of the device of the present invention;
FIG. 2 is a diagram for explaining the principle of the device of the present invention;
FIG. 3 is a diagram for explaining the principle of the device of the present invention;
FIG. 4 is a diagram for explaining the principle of the device of the present invention;
FIG. 5 is a block diagram of an active silencer according to the first embodiment of the present invention.
FIG. 6 is a block diagram of an active silencer according to a second embodiment of the present invention.
FIG. 7 is a block diagram of an active silencer according to a third embodiment of the present invention.
FIG. 8 is a block diagram of an active silencer according to a fourth embodiment of the present invention.
FIG. 9 is a block diagram of an active silencer according to a fifth embodiment of the present invention.
FIG. 10 is a block diagram of an active silencer according to a sixth embodiment of the present invention.
FIG. 11 is a power distribution characteristic diagram showing a state of distribution of acoustic power in the vicinity region with the sound radiation source as the origin.
FIG. 12 is a power distribution characteristic diagram showing the distribution state of acoustic power in the vicinity region with the sound radiation source as the origin.
FIG. 13 is a block diagram of an active silencer according to a seventh embodiment of the present invention.
14 is a schematic view in the direction of the arrow along the line HH in FIG.
FIG. 15 is a diagram showing the difference in the silencing effect due to the difference in the evaluation microphone position when d = 0.3 m is set in the embodiment.
FIG. 16 is a diagram showing the difference in the silencing effect due to the difference in the evaluation microphone position when d = 0.16 m is set in the same example.
FIG. 17 is a layout of the main part of an active silencer according to an eighth embodiment of the present invention.
FIG. 18 is a block diagram of an active silencer according to a ninth embodiment of the present invention.
FIG. 19 is a schematic view in the direction of the arrow along the line II in FIG.
FIG. 20 is a block diagram of an active silencer according to a tenth embodiment of the present invention.
FIG. 21 is a schematic view taken in the direction of the arrow along the line JJ in FIG. 20;
FIG. 22 is a diagram showing the difference in the silencing effect due to the difference in the evaluation microphone position in the same example.
FIG. 23 is a diagram showing the difference in the silencing effect due to the difference in the evaluation microphone position in the same example.
FIG. 24 is a diagram showing phase characteristics with respect to a sound source according to a difference in evaluation microphone position in the same example;
FIG. 25 is a diagram showing volume velocity ratio characteristics depending on the evaluation microphone position in the same example;
FIG. 26 is a diagram showing the difference in the silencing effect due to the difference in the evaluation microphone position when d = 0.22 m is set in the embodiment.
FIG. 27 is a diagram showing the difference in the silencing effect due to the difference in the evaluation microphone position when d = 0.3 m is set in the embodiment.
FIG. 28 is a layout of the main part of an active silencer according to an eleventh embodiment of the present invention.
FIG. 29 is a block diagram of an active silencer according to a twelfth embodiment of the present invention.
30 is a schematic view in the direction of the arrow along the line KK in FIG. 29;
FIG. 31 is a diagram showing measured values of the silencing effect due to the difference in the evaluation microphone position of the apparatus shown in FIG. 20 and FIG. 28;
FIG. 32 is a diagram showing measured values of the silencing effect due to the difference in the evaluation microphone position of the apparatus shown in FIG. 20 and FIG. 28;
FIG. 33 is an explanatory diagram of a conventional passive silencing process.
FIG. 34 is a diagram showing an example of a conventional active silencer
FIG. 35 is a block diagram showing another example of a conventional active silencer.
FIG. 36 is an explanatory diagram of a failure example in the conventional active silencer.
[Explanation of symbols]
21 ... Controlled device 22 ... Sensing unit
23 ... Control coefficient calculation unit 24 ... Control coefficient product-sum calculation unit (A-FIR)
25 ... Additional sound source section (FIR) 26a, 26b ... Additional sound source
27 ... Evaluation microphone as sound detection means 28 ... Control system
30 ... Duct 31 ... Duct opening (sound source)
32 ... Center of sound source 33a, 33b ... Cover member

Claims (5)

A plurality of additional sound sources for radiating sound having the same phase and interfering with sound radiated three-dimensionally from the sound source;
Sound detection means provided in a space through which the sound emitted from the sound source is transmitted;
Control means for controlling each additional sound source to minimize the output of the sound detection means,
Each of the additional sound sources and the sound detection means is arranged so that the sound source, the additional sound source, and the sound detection means are positioned at each vertex of an equilateral triangle, respectively. A plurality of additional sound sources for radiating sound having the same phase with each other and being arranged around the sound source to interfere with the sound emitted three-dimensionally from the sound source;
Sound detection means provided in a space through which the sound emitted from the sound source is transmitted;
Control means for controlling the additional sound source to minimize the output of the sound detection means,
The distance between the sound source and each additional sound source is set to a substantially constant value d, the distance between each additional sound source and the sound detecting means is set to a substantially constant value h, and An active silencer, wherein a distance between a sound source and the sound detection means is set equal to the value h. The distance d between the sound source and each additional sound source and the distance h between each additional sound source and the sound detection means satisfy a relationship of d <h. The active silencer as described. 2 that can be synchronously controlled to emit sound that interferes with the sound that is three-dimensionally radiated from the sound source, disposed at equidistant positions on both sides of the sound source with the vibration surface positioned on a line passing through the vibration surface of the sound source. A plurality of additional sound sources, sound detection means arranged on the line passing through the vibration surface of the sound source, and control means for controlling each of the additional sound sources to minimize the output of the sound detection means. An active silencer characterized by that. The active silencer according to any one of claims 1 to 4, wherein each additional sound source is provided with guide means for guiding and radiating sound power to a predetermined area.

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